The sensory transduction system of Phycomyces blakesleeanus has been studied for some time with the major emphasis placed on characterizing its behavior upon light stimulation. Mutants with modified behavior have become available. Phycomyces may also be a good model for hormonal and developmental systems. The possible role of cyclic nucleotides will be further elucidated in this study. Changes in cyclic nucleotides during the behavioral responses and during development will be determined in wild type and mutants. Differences in adenylate cyclase activity will also be examined. Another topic will be the sensitivity of Phycomyces adenylate cyclase to catecholamines and their antagonists and agonists. Cyclic nucleotide phosphodiesterase and protein kinase will be less extensively investigated. Light activation of cyclase and phosphodiesterase will be characterized, especially the action spectrum. Enhanced activity may be diagnostic for the elusive photoreceptor. The overall objective is to dissect the sensory pathway by establishing the position of the cyclic nucleotide system in the pathway from stimulus to response.